From the perspective of energy and environmental concerns, technologies that convert solar energy into hydrogen energy by the electrolysis of water using a photocatalyst have attracted attention. 1.23 V or more of an electrolytic voltage is theoretically required in a reaction of the electrolysis of water. Therefore, it is desirable to create a photoelectrode to enable the electrolysis of water with a low voltage. Typically, in producing the photoelectrode, a method of coating a substrate or the like with a photocatalyst is employed. Micronization of the photocatalyst has been studied to obtain a homogeneous thin film of the photocatalyst.
Micronization of BiVO4 has been studied in bismuth vanadate (BiVO4), which is known to have a photocatalytic activity. For example, a method of irradiating a suspension with laser light under agitation, the suspension being obtained so that BiVO4 powder having an average particle diameter of about 10 to 20 μm is dispersed in an aqueous medium, to obtain minute particles of BiVO4 having an average particle diameter of 1 μm or less, to manufacture a colloidal dispersion, has been proposed (see Patent Document 1). Furthermore, a method of manufacturing fine BiVO4 powder having a BET surface area of about 0.3 m2 g−1 by making NH4VO3 and Bi(NO3)3 to react with each other under the presence of urea has been proposed (see Patent Document 2).
Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2008-019156
Patent Document 2: Japanese Unexamined Patent Application, Publication No. 2004-024936